Field
Embodiments of the present disclosure generally relate to processing of natural gas and, more specifically relate to real-time monitoring of natural gas composition during a natural gas upgrading operation.
Technical Background
The demand for natural gas is continually increasing at least in part because of its usefulness to produce energy as well as its applicability to additional applications in the petrochemicals industry. Many new fields of natural gas recently discovered in locations such as Saudi Arabia contain high levels of acid gases (hydrogen sulfide and carbon dioxide) and nitrogen. The high content of acid gases and nitrogen in natural gas limits its use as a source of energy due to low BTU values as the quality and market value of produced natural gas depends on its composition. The presence of high content of nitrogen, hydrogen sulfide and/or carbon dioxide is one of the main reasons for the non-applicability of a natural gas in producing energy and/or applications in the petrochemicals industry. The abundance of non-useful natural gas produces new opportunities to make the non-useful natural gas useful by selectively removing components such as nitrogen, moisture and acid gases. Selective removal of these components has been achieved by cryogenic technique, use of membranes, or pressure swing adsorption (PSA) techniques. In some cases a combination of two or three techniques has been applied to achieve desired results. The selective removal process of undesired components from the bulk gas is assisted by reliable and continuous monitoring of the process. Such monitoring can be accomplished by using techniques such as gas chromatograph or other spectroscopic or laser based techniques. During the development of a new or improved process, it is essential to know the performance of the upgrading module by precisely determining the composition of incoming and outgoing gaseous products on a continuous basis.
Traditional gas chromatograph techniques have the accuracy limitation of more than ±3%, when used in series; meaning if two different gas chromatographs are used on a single application, at least a ±3% variation is anticipated between the results for the same gas sample. The goal of upgrading of natural gas involves use of cryogenic, membrane based or similar techniques, in which case, the processing results are dependent on the temperature, pressure, flow, and presence of moisture in the gas stream. Any change in the process upgrading configuration can result in a 1 to 2 percent improvement in the composition of the processed gas. Monitoring of such minute change in the composition of the processed gas is important in making a selection of the most appropriate membrane or modifying an existing membrane or similar upgrading technique.
Gas chromatographs and other analyzer techniques have been in use since the early stages of gas upgrading processes, yet the conventional use of multiple gas chromatographs lack accuracy. Hence present systems are unable to differentiate minute changes in the composition of the natural gas while being processed. Accordingly, ongoing needs exist for an improved method of determining minute changes in the composition in real time of natural gas during processing is desired.